Example 1: PC Card alone
Output power for a Lucent/Orinoco/Agere/Avaya 802.11b PC card is 15 dBm. If there is no external antenna then that's the answer. 15dbm.
Example 2: PC Card with 14 dBi external antenna and 50 ft of LMR400
Assumed total lost for a pigtail adapter is 0.5 dB. Loss for each connector on LMR400 is 0.5 dB.
+ PC card - pigtail adapter - connector - 50 ft LMR400 - connector + 14 dBi antenna = ? Total output power
Substitute the six items above with their 'db-counterparts' with + for things that add power and - for losses
15 dBm - 0.5 dB - 0.5dB - 3.3 dB -0.5 dB + 14 dBi = 24.7 dBm
Example 3: PC Card with 24 dBi external antenna and 50 ft of LMR400
15 dBm - 0.5 dB - 0.5dB - 3.3 dB -0.5 dB + 24 dBi = 34.7 dBm